Over the years, preformed wall finishing materials such as dry wall gypsum board (commonly referred to as "dry wall"), particle board, masonite and other particulate or fibrous materials have largely replaced plastered walls in commercial and residential buildings.
As opposed to plaster which is applied to a lath base in a semi-liquid state, wallboard is secured to the supporting frame structure by the use of nails or screws. For example, wallboard is attached to wooden thin-wall metal studs by the use of self-tapping "drywall screws".
Drywall is comprised of a sandwich panel of paper exteriors having a gypsum core. The drywall screw is usually comprised of a bugle head and a threaded shank (either with single lead or twin lead threads) having a sharp point or a point with selfdrilling drill flutes for heavier gauge metal studs. Commercially, the screws are inserted by electrically-powered screw guns which rotate at speeds above 2,000 revolutions per minute or greater, and the screw point thus moves rapidly through the soft gypsum board and the outer layers of paper. However, when the screw reaches the metal or wooden stud any hesitation in the axial travel of the drywall screw, while the screw gun continues to rotate, will strip any threads which have been tapped in the gypsum board and, in effect, convert the fastener to a screw auger which reams the gypsum from around the shaft of the fastener, thereby weakening the support for the paper surface. Accordingly, it is not uncommon that the head of the fastener punctures the paper exterior. As the paper provides the integral strength of the wallboard, the breaking of the paper over the screw head weakens the fastening. According to standard building codes, the fastening is deemed acceptable only when the dry wallboard has been attached firmly to the supporting stud without spacing voids, with the head of the drywall screws only slightly countersunk. Further, codes require that the fastener, when seated, does not cut underneath the head for the full 360 degrees of the head diameter. In commercial applications, whenever excessive gypsum has been augered from the drywall board or the head of the dry wall screw fails to properly tuck the exterior surface paper for any reason, additional labor is required to properly secure the wallboard-supporting structure, and to properly repair blemishes formed in the paper surface.
Further, it is not uncommon to find paper burrs around the head of a seated drywall screw which result from a tendency of the outer paper layer to "ride" the inclined plane of the bugle head and overlap the top surface of the seated screw.
Numerous approaches to correct these problems have been taken. For example, U.S. Pat. Nos. 3,703,843; 3,861,269 and Re. 28,111 to Laverty teach a drywall screw having a shank with a first continuous thread from the point to the head and a second parallel thread intermediate the first thread only on the point end of the fastener. The thread toward the head end of the shank has increased thread spacing between adjacent thread portions and a greater crest diameter than the initial threads, and this construction is said to result in less deformation of the particulate wallboard filler and increased holding power. U.S. Pat. No. 3,942,405 to Wagner describes a screw having multiple threads so that the initial penetration of the screw into the supporting structure is accelerated.